I have a project I've been considering for a bit now, and I need some insight on it. I have a pair of older speakers, Yamaha NS-A636 bookshelf units. I got them sometime in 1997, I think, from some discount catalog for $79 if memory serves. They are sturdy speakers and I'm using them as TV speakers for the den.

The problem is they've always been muddy sounding. I've read many reviews of the speaker and it's a common complaint. The speaker is fairly bare bones. The inside of the speaker(s) is empty. I've heard you can improve the sound of speakers by adding polyester "fill" to them. There's other theories, like fiberglass insulation, foam sheets on the inside walls of the speaker, carpet padding, carpet itself, wool sheets, and other assorted materials.

Has anyone ever tried anything like this with an old pair of speakers, or even with the 636 series? If so, any advice? I'd really like to clean them up a bit and dress up the sound. Thanks!

Adding polyfill will have to some extent the same effect as a larger enclosure. It may reduce "boomy-ness" caused by unwanted resonance. The only way to find out if it will sound better is to try but I wouldn't expect miracles.

Adding fill will definitely help the sound. You need something inside there to absorb the sound waves coming off the back off the speaker cone. I used R-11 fiberglass insulation inside the speakers and subwoofer I built and it makes a major difference in the sound quality. Polyfill will work similarly. Pack it in there loosely, and make sure whatever you're using won't touch the driver itself. Also, before you put the driver back in, make sure the enclosure is well sealed along all seams; air leaks will cause problems such as whistling sounds.

I used some polyfill when I built my Overnight Sensations. It's really inexpensive stuff, so if I were you, I would buy a bag and then just experiment to see how much you need to get the sound you want. I would guess that you'd end up filling about 1/5 to 1/3 the remaining volume of the box with polyfill.

Neil Stephenson wrote:The danger lies not in the machine itself but in the user's failure to envision the full consequences of the instructions he gives to it.

There are two modifications that would improve the sound -- the fiberglass or polyfill approach will help with the bass range, since it works by reducing the standing waves that form within the cabinet.

For the upper-bass and midrage frequencies, you need acoustic foam with the usual "eggcrate" anechoic surface. The favorite supplier for all things DIY audio is Parts Express, and a suitable block of foam is available here. One sheet per cabinet should do the trick. Cut sections and glue them to the interior walls. The front baffle can be omitted.

The result of completing these mods should be a speaker that sounds noticeably tighter and more defined across the audio spectrum, but which will also seem to lose some of its former bass response. Once you adjust to the change in the sound, and/or adjust your tone controls to compensate, they should be significantly improved.

However, there are two potential problems that won't be solved:

1) Woofer surrounds -- A quick GIS suggests these units use foam. Are they getting dry, or already starting to crack and break up? If so, rapid deterioration will follow.

2) Crossover -- most cheaper commercial speakers use very cheap crossover designs and have electrolytic capacitors that dry out with age.

There are repairs that can be done, but if it looks like you're going to be spending at least $50 to resurrect an old and relatively low-quality speaker system, you might want to look into the Overnight Sensations that alloyD linked. The complete kit, assuming you can do some basic soldering, is $120. They will completely blow away the Yamaha set, and you have the luxury of choosing how to finish the cabinet.

I've done what Ludi has said to do - a foam anechoic surface. I did it using plain old sofa foam and cutting a block in half with a sawtooth pattern, made a pretty big difference to the resonant boomy/muddiness of the speakers.

Some people ask me why I have always enclosed my signature in spoiler tags; There is a good reason for that, but I can't elaborate without giving away the plot twist.

Chrispy_ wrote:I've done what Ludi has said to do - a foam anechoic surface. I did it using plain old sofa foam and cutting a block in half with a sawtooth pattern, made a pretty big difference to the resonant boomy/muddiness of the speakers.

That can work, but with a caveat -- many upholstery foams and similar materials (such as carpet padding) are not particularly good at absorbing audio frequencies. You can still cut them to form a disruptive surface, but they will not damp as well as true acoustic foam, and will also reduce the cabinet's effective volume.

Deanjo wrote:You shouldNOT use fibreglass insulation for filler. What happens is the glass particulates often find their way into the spider and voice coil causing rubbing and wear.

I've been using three speakers with fiberglass in them since 1996, without issue. It was the recommended filler material according to the Loudspeaker Design Cookbook.

Regardless, polyfill is admittedly easier to work with and cheaper.

Oh I know the LDC all to well. It also has a bunch of outdated information and was written before most speakers had a vented coil. Also using fibreglass insulation is a large health hazard when used in a vented enclosure. There is a reason why masks are required when handling the stuff.

Deanjo wrote:You shouldNOT use fibreglass insulation for filler. What happens is the glass particulates often find their way into the spider and voice coil causing rubbing and wear.

I've been using three speakers with fiberglass in them since 1996, without issue. It was the recommended filler material according to the Loudspeaker Design Cookbook.

Regardless, polyfill is admittedly easier to work with and cheaper.

Oh I know the LDC all to well. It also has a bunch of outdated information and was written before most speakers had a vented coil. Also using fibreglass insulation is a large health hazard when used in a vented enclosure. There is a reason why masks are required when handling the stuff.

I built fish boats for a while, fiberglass ones. You cannot inhale normal fiberglass, it's long fibers just hang up in your nose and respiratory system. Now fiberglass that has been powdered and grindings from set up fiberglass parts can be a real problem.

ludi wrote:There are two modifications that would improve the sound -- the fiberglass or polyfill approach will help with the bass range, since it works by reducing the standing waves that form within the cabinet.

For the upper-bass and midrage frequencies, you need acoustic foam with the usual "eggcrate" anechoic surface. The favorite supplier for all things DIY audio is Parts Express, and a suitable block of foam is available here. One sheet per cabinet should do the trick. Cut sections and glue them to the interior walls. The front baffle can be omitted.

The result of completing these mods should be a speaker that sounds noticeably tighter and more defined across the audio spectrum, but which will also seem to lose some of its former bass response. Once you adjust to the change in the sound, and/or adjust your tone controls to compensate, they should be significantly improved.

However, there are two potential problems that won't be solved:

1) Woofer surrounds -- A quick GIS suggests these units use foam. Are they getting dry, or already starting to crack and break up? If so, rapid deterioration will follow.

2) Crossover -- most cheaper commercial speakers use very cheap crossover designs and have electrolytic capacitors that dry out with age.

There are repairs that can be done, but if it looks like you're going to be spending at least $50 to resurrect an old and relatively low-quality speaker system, you might want to look into the Overnight Sensations that alloyD linked. The complete kit, assuming you can do some basic soldering, is $120. They will completely blow away the Yamaha set, and you have the luxury of choosing how to finish the cabinet.

Thanks Ludi! Really, I'm just tinkering with the speakers. I've never really used them much in the years that I've had them. They've mostly just done light TV duty and that's about it. They really don't sound all that great, so I've never been tempted to use them for serious music listening. They're in great shape for being as old as they are. I'd like to improve them if it's not that difficult and isn't expensive. I had read about speakers sounding better with filler, and I know higher end speakers come with sound dampening.

I checked the speakers, hoping the back has screws that would allow me to remove the back panel. There's none, so it looks like accessing the interior of the speakers is going to be a bit of a pain. I guess I am supposed to go in through the woofer opening. The crossovers are just caps. I'm guessing I need to replace those?

PenGun wrote: I built fish boats for a while, fiberglass ones. You cannot inhale normal fiberglass, it's long fibers just hang up in your nose and respiratory system. Now fiberglass that has been powdered and grindings from set up fiberglass parts can be a real problem.

Helped run a fibreglass factory myself with my brother inlaw (building/designing boats, water/septic tanks, van camper tops, etc). As you should know by building fibreglass boats that fibreglass comes in many forms (not only in fibre spools which is then fed into the chop gun where it is mixed with the catalyst and resin and chopped up into smaller strands and millions of microscopic glass particles in the process). Fibreglass insulation itself contains many many many small glass particles.

The Swamp wrote:I checked the speakers, hoping the back has screws that would allow me to remove the back panel. There's none, so it looks like accessing the interior of the speakers is going to be a bit of a pain. I guess I am supposed to go in through the woofer opening. The crossovers are just caps. I'm guessing I need to replace those?

Yeah, the woofer hole is usually the easiest to work through. For significant modding it's often advisable to pull out all of the drivers and electrical hardware, then reinstall when done. Be vigilant with the screwdriver, though, many a speaker driver has been punctured by a screwdriver slip. I usually hold the shaft of the driver (manual or electric) against the screw head with a gloved hand, while operating it with the other hand. Also take careful pictures or notes of wire colors and polarities going into each driver so that you can correctly reconnect everything later.

The crossovers can be refurbished if you wish, for cost reasons you probably want to just replace "like in kind" with bipolar electrolytics at, or as close as possible, to the original values. Parts Express does have a whole selection of metalized polypropylene units if you want to get a bit more exotic, but now you're talking about $3-6 per unit instead of $0.50-1.50.

PenGun wrote: I built fish boats for a while, fiberglass ones. You cannot inhale normal fiberglass, it's long fibers just hang up in your nose and respiratory system. Now fiberglass that has been powdered and grindings from set up fiberglass parts can be a real problem.

Helped run a fibreglass factory myself with my brother inlaw (building/designing boats, water/septic tanks, van camper tops, etc). As you should know by building fibreglass boats that fibreglass comes in many forms (not only in fibre spools which is then fed into the chop gun where it is mixed with the catalyst and resin and chopped up into smaller strands and millions of microscopic glass particles in the process). Fibreglass insulation itself contains many many many small glass particles.

All depends on what you are building, the boats we hand laid the matt, fine weave or course weave (depending on the area of coverage due to different strength needs). Used the chop gun on those just for dispensing the resin and catalyst. Building the tanks however would be cost prohibitive to utilize hand layup (not to mention extremely time consuming). Eventually got out of boats (the money is better in tanks and such) and all the smaller stuff we moved to a injection application.

This is my first post on this site. I build and modify speakers for grins. I built this PC for grins. I build and modify amps for grins, too. I build and modify a lot. I grin a lot

Tomorrow is my 67th BD... hence my [ g33zr ].

Enuf about ME! ME! ME!

When you remove the woofer to get into the guts of the beast, make sure you are using a screwdriver that actually fits the screws, tightly. No sense poking a hole in the unit to save the time and money of buying a screwdriver... you will live a long, long time. Buying a good tool is an investment, even if you are just messing with some old cheap speex, do it right.

When you get it open, before you take it all apart, draw yourself a diagram showing the connections. You can take a picture, but, it helps to understand what you are doing to look at the actual live unit and figure out what goes where. Why can wait.

OK, your 636 is a three way in a fairly heavy box. It has potential.

I have some Yamahas. They are very pleasant. My wife has a Yamaha synth. It has an external amp and speakers that I built for grins...

Before I go screaming into the dawn, please tell me what makes you think they are not clear? Have you attached them to something other than a TV? TVs are not awesome audio. They are TVs. No sense stuffing the speakers, or anything, if the TV is not giving them a clean signal.

Hook them up to an actual stereo music system and listen. Maybe the problem is not the speakers?

______

OK, so, stuffing is something you can do. Do not use 'glass. It is cheap to get, but dreadful to get rid of, am I being clear, here?

Wool yarn is superb, and pretty cheap at a big box store, especially since you do not care about the color. Just get whatever is on sale. Or, you can use cut up old wool sweaters or wool blankets. Wash whatever you use in Woolite and dry thoroughly before putting them in. Sweat and dirt are not acoustically attractive.

The other easy thing to do is put some mixed pieces of wood or other stuff on the bottom, to break up standing waves. Then put the stuffing in on top. Do not cram the box full, leave open spaces around the drivers. It is OK to add a couple of dowels (or something - bent wire coat hangers?) inside between the walls to keep the stuffing from falling on the drivers.

If you want to get into it, you can saw the back wall off the box, at an angle, then turn it upside down and screw/glue it back on to make the box not all symmetrical. Yes, rectangular boxes are cheap to build and look attractive. They do not sound all that great

Thanks, g33zr. Actually, the speakers are connected to a Pioneer receiver, so they're getting a good signal. The speakers themselves are pretty simple. Most of the weight seems to be the cabinet itself, which I suspected was empty.

I was able to get a huge sheet of foam carpet padding from a local flooring store. I opened up one of the Yamaha speakers by removing the woofer. There's not much to the woofer. It was much lighter than I expected, with a fairly small magnet. I unplugged it and looked inside the cabinet. Sure enough, it was completely empty. Shouting into it created a loud pronounced echo/reverb. I was thinking that cannot be very good. I cut a fitted sheet of padding and glued it to the back wall, then rolled up two sheets (top to bottom length) and put them into the enclosure. The echo/reverb was gone after that.

I put the speaker back together and tried it out. It does seem to sound a bit richer and fuller, but it was hard to tell from just the TV signal. I've been thinking of getting a pair of woofers from Parts Express. I think even cheap ones would be an improvement over the ones in there now. I'd like to use them for surrounds, maybe.

The Swamp wrote:I put the speaker back together and tried it out. It does seem to sound a bit richer and fuller, but it was hard to tell from just the TV signal. I've been thinking of getting a pair of woofers from Parts Express. I think even cheap ones would be an improvement over the ones in there now. I'd like to use them for surrounds, maybe.

I did that with a pair of speakers given to me by a friend. Both woofers were blown, so I ordered some appropriate ones from Parts Express and screwed 'em in. They sounded just fine. More tinkering wasn't worth the time per improvement ratio. I think the total cost was under $100.

If the speaker have a known issue such as you described in the OP, I suspect there's a dozen posts or so about what replacement woofers will work well with that enclosure. That way you won't have to go about calculating internal cavity volumes and finding an online acoustic modeling app, etc.

Welcome to the Tech Report G33zr!

If there is one thing a remote-controlled, silent and unseeable surveillance/killing machine needs, it’s more whimsy. -- Marcus

The Swamp wrote:I was able to get a huge sheet of foam carpet padding from a local flooring store. I opened up one of the Yamaha speakers by removing the woofer. There's not much to the woofer. It was much lighter than I expected, with a fairly small magnet. I unplugged it and looked inside the cabinet. Sure enough, it was completely empty. Shouting into it created a loud pronounced echo/reverb. I was thinking that cannot be very good. I cut a fitted sheet of padding and glued it to the back wall, then rolled up two sheets (top to bottom length) and put them into the enclosure. The echo/reverb was gone after that.

Carpet padding is a fairly so-so material, it will mute things a bit but not a lot, and it tends to reduce the effective enclosure volume (which shifts the woofer's lower resonant upward).

One nice thing about Parts Express is that most of their bass drivers include estimated enclosure sizes. If you decide to replace the woofers, make sure the replacements have a recommended volume fairly close to the internal volume of your existing cabinets. Too much, and you may crash the voice coils from over-excursion; too little, and the lower 3dB roll-off point will begin to shift upward while possibly also giving rise to an exaggerated peak in the mid-bass range.

I knew the padding was not the best material, but that can be offset by using more of it. The echo in the cabinet was pretty sharp since it's a fairly deep cabinet. I was surprised about how light the woofer was. There's just not much to it at all. I'm guessing the other components are also not of...ahem... great quality as well?

The Swamp wrote:I knew the padding was not the best material, but that can be offset by using more of it. The echo in the cabinet was pretty sharp since it's a fairly deep cabinet. I was surprised about how light the woofer was. There's just not much to it at all. I'm guessing the other components are also not of...ahem... great quality as well?

These appear to have been a mid-grade speaker in 1997, so I wouldn't expect extraordinary quality. However, woofers that are higher efficiency and/or designed purely for sealed-box applications tend to be smaller and lighter than woofers that are designed to also support ported-enclosure applications, particularly once you start comparing drivers intended for car audio.

Also, don't forget that when you're listening to your speakers, you're listening to your listening room too. Have you tried moving the speakers closer or farther away from the wall? That affects the bass response a great deal as it changes the frequency of the standing wave between walls and speaker. There are other things you can do, if only as an experiment. Open all the doors and windows, including cabinet doors - this should reduce or even remove resonance at certain frequencies. Bring all the carpets you have in the house into the room, hang some on the walls somehow. Listen to the same setup in another room or outside the house if it's possible. With some music you know well, listen carefully to individual notes on bass instruments. If some are too loud, muddy, or reverberate across the room, it may be the room's fault, and rooms often have narrow resonances that turn certain musical notes into a mess but don't affect others. You may not have access to measuring equipment but such experiments can still reveal some problems, and help find out if it's the speakers or the room that's to blame.

Thanks, Pen. It wasn't until I started digging around that I discovered just how complex it is to figure out how to design a crossover. There are so many variables, it seems to be an art form to get it right depending on the speaker components and box design. I can see now why there are whole companies that do just speaker design and build. I'm guessing the woofers in my speakers are full range since they don't have a low-pass filter on them. The caps on the mid and tweeter are almost 20 years old, so I'm going to replace those to at least bring the speakers to where they were when they were new.